This work is designed to ascertain the apoprotein subunit structure of human low density lipoproteins (LDL), and to isolate and quantitate lipoprotein subpopulations in normal and hyperlipoproteinemic individuals. Each of the lipoprotein classes will be isolated by preparative ultracentrifugation. LDL apoprotein subunits will be prepared as previously reported and will be characterized by finger printing, partial sequence analysis and by immunochemical methods. Lipoprotein subpopulations will also be characterized and quantitated by immunochemical methods, similar to those previously reported. The significance of this work is that the results should lead to understanding of the control mechanism of lipid transport.